A variety of methods and devices exist for obtaining and dispensing small amounts of liquids that have found use in a variety of applications. However, few methods and devices exist for manipulating small amounts (e.g., less than about 25, 10, 5, or 1 mg) of solids (e.g., powders). In the laboratory, such small amounts of solids are often dispensed by hand using a highly accurate scale. Unfortunately, such methods are not amenable to the rapid or automated manipulation of compounds, as they are tedious, time consuming, and prone to error.
Recently, methods and systems have been disclosed for the preparation and analysis of arrays of samples, each of which can contain very small amounts of one or more compounds. See e.g., International Publication WO01/51919, published on Jul. 19, 2001. In such applications, it is often desirable to rapidly and accurately measure and dispense small amounts of solids. In some circumstances, this can be done by dissolving a compound in a solvent to provide a solution of known concentration, dispensing controlled amounts of that solution using micropipettors, and then evaporating the solvent. In certain applications, however, it is necessary that a solid compound be manipulated in a manner that does not substantially affect its physical form. For example, if the crystallinity of a solid is important, it is desirable to measure and dispense the solid in a manner that does not affect its crystalline form (e.g., its crystal structure and habit). Similarly, if the amorphous nature (e.g., average particle size and distribution of particle sizes) of a solid is important, it is preferred that the methods and devices used to manipulate the solid do not substantially affect that quality. Physical characteristics such as these cannot be controlled using solution-based dispensing techniques.
A need therefore exists for methods and devices that can be used to rapidly and accurately dispense small amounts of solids. A need also exists for methods and devices that can be used to manipulate solids without substantially affecting their form.